In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The native heart valves are identified as the aortic, mitral (or bicuspid), tricuspid, and pulmonary, and each is mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice. FIG. 1 shows a schematic representation of the anatomic orientation of the heart, illustrating the atrioventricular (AV) junctions within the heart and the body in the left anterior oblique projection. The body is viewed in the upright position and has three orthogonal axes: superior-inferior, posterior-anterior, and right-left.
FIG. 2 is a cutaway view of the heart from the front, or anterior, perspective, with most of the primary structures marked. As is well known, the pathway of blood in the heart is from the right atrium to the right ventricle through the tricuspid valve, to and from the lungs, and from the left atrium to the left ventricle through the mitral valve. The present application has particular relevance to the repair of the mitral valve, which regulates blood flow between the left atrium and left ventricle, although certain aspects may apply to repair of other of the heart valves. The tricuspid and mitral valves together define the AV junctions.
Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood through the valve when the valve is closed (regurgitation). Valve disease can be severely debilitating and even fatal if left untreated.
Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. One repair technique is remodeling annuloplasty, in which the deformed valve annulus is reshaped by attaching a prosthetic annuloplasty repair segment or ring to the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation of the valve leaflets and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow. Annuloplasty ring repair is currently performed on both mitral and tricuspid valves, through both traditional surgical procedures as well as minimally invasive approaches.
An annuloplasty ring typically comprises an inner substrate of a metal such as rods or bands of stainless steel or titanium, or a flexible material such as silicone rubber or Dacron cordage, covered with a biocompatible fabric or cloth to allow the ring to be sutured to the fibrous annulus tissue. Annuloplasty rings may be stiff or flexible, split or continuous, and may have a variety of shapes, including circular, D-shaped, C-shaped, or kidney-shaped. Examples are seen in U.S. Pat. Nos. 5,041,130, 5,104,407, 5,201,880, 5,258,021, 5,607,471, 6,187,040, and 6,908,482. Annuloplasty rings are available in a variety of different sizes to accommodate differences in the sizes of patients' native valves. The correct size of prosthetic annuloplasty ring to use for a given patient must be determined for each repair procedure performed.
To perform successful valve replacement or annuloplasty surgeries, the size of the valve annulus must be accurately measured. In conventional methods, sizing may be achieved by measuring the width and height of the anterior leaflet of the mitral valve, for example, by using a valve sizer or template, which resembles the shape of the annulus and is provided in various incremental sizes corresponding to the stepped valve or repair ring sizes. In order to use a sizing template, a surgeon or other user estimates the valve annulus size and selects the template accordingly. The template is guided into proximity of the annulus with a handle. If the template is judged to be the incorrect size, it is withdrawn, and replaced by a different template. Once the size of the annulus has been determined, a properly sized valve or annuloplasty repair ring is selected and implanted.
Thus, during a heart valve repair procedure, the size of a patient's native heart valve annulus is typically determined by holding various sizers adjacent the native annulus, where each of the various sizers represents an available prosthetic repair ring device size. The surgeon then determines which of the sizers is closest to the patient's native annulus, generally with a best guess visual determination of which sizer looks “correct.” A surgeon typically must try several different sizers, sometimes more than once, and perhaps even test one or more repair ring sizes before being able to determine the correct repair ring size for a given patient. This trial-and-error sizing technique is imprecise, tedious, and time-consuming. Furthermore, the surgical field may be cluttered with several different static sizers.
Less invasive annuloplasty procedures have been developed in recent years, but traditional annuloplasty and valve sizing and holding instruments are designed for use with open-chest surgery that exposes the implant site. Currently, sizers are dimensionally the same as the repair rings they represent. Because of this, it can be difficult to insert the sizers through minimally invasive surgical incisions, such as thoracotomies. Inserting several sizers, one at a time, through a small incision can be particularly time-consuming and frustrating for surgeons.
Thus, for these and other reasons, there remains a need for an improved sizer and method of sizing a patient's valve annulus for annuloplasty repair.